JP2020536448A - Remote radio head, beamforming method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RRH (Remote Radio Head) capable of adaptively adjusting coverage according to traffic demand by a mechanically efficient method. In a wireless communication system that provides a service to at least one user terminal, a plurality of RRHs having a plurality of antennas capable of generating a plurality of analog beams are used in wireless communication that provides a service to at least one user terminal. It is equipped with multiple antennas that generate the analog beam of. RRH has a metric calculator and a beam former. The metric calculator is configured to calculate at least one metric indicating traffic demand as a function in the spatial direction by using the signal of each RF chain (Radio Frequency Chain). The beam molder is configured to generate an analog beam in the spatial direction of high traffic demand based on at least one calculated metric. [Selection diagram] Fig. 3

Description

The present invention relates to a remote radio head (RRH: Remote Radio Head), a beamforming method, and a storage medium in which the program thereof is stored. In particular, it relates to a remote radio head for estimating the demand for traffic, a beamforming method, and a storage medium for storing a program.

Base Transceiver Stations (BTSs) with remote radio heads (RRHs) are of great help to the problem of mobile operators pursuing performance and efficiency at low cost. The "remote" of a remote radio head means that it is usually located at some physical distance from the Base Band Unit (BBU). The remote radio head is mainly included in the RF (Radio Frequency) function of the radio base station. In addition, the remote radio head is connected by a bidirectional radio interface to a portion of the baseband unit that performs the remaining baseband processing.

In general, each remote radio head covers a wider area of the azimuthal surface and a relatively narrow area of the elevational surface. Therefore, the telecommunications carrier can optimize the tilt angle within a range specified to some extent by RET (Remote Electrical Tilt), which is a feature of the remote wireless head. However, the RET needs to be constantly monitored by humans using some external device. Moreover, the RET cannot adapt to dynamically changing patterns of traffic within the area covered by the radio base station.

By applying three-dimensional (3D) beamforming with a large-scale array active antenna and MIMO (Multi-Input Multi-Output) mechanism, both azimuth and elevation planes are dynamic. Coverage can be adjusted adaptively to changes in traffic patterns. However, such a mechanism requires computationally intensive (heavy) signal processing. Typically, the presence of numerous RF circuits within the remote radio head adds an order of magnitude (by ten-folds) complexity to the hardware and software. Furthermore, such a mechanism requires fine coordination between beamforming and user scheduling (see Patent Document 1). And that results in a seriously higher overhead due to the coordinated coordination between the upper and lower layers of the wireless communication system. In addition to these, such mechanisms cannot meet modern high-speed wireless communication standards and hardware.

Patent Document 3 discloses an all-digital beamforming mechanism for estimating network traffic (FIG. 8). In this document, the approach angle (AoA: Angle Of Arrival) is estimated using only the upstream signal.

In recent years, the literature has proposed new approaches to adaptively adjust coverage in both azimuth and elevation. The approach is based on integrating phased array antennas into their respective RF circuits and is suitable for directional analog beams that match communication demand and / or user density distribution within coverage. Weighting is applied. By doing so, it is also possible to add the gain of analog beamforming to the commonly used digital precoding. Such a mechanism is referred to as hybrid analog-digital beamforming in the literature of wireless and mobile communications.

The hybrid analog-digital beamforming mechanism applies two levels of beamforming. That is, coarse-level analog beamforming using a phased array antenna and fine-level digital beamforming using baseband processing. In this document, a method of comprehensively optimizing digital precoding and analog beamforming using CSI (Channel State Information) from a baseband unit is being studied. Such a technique requires tight integration of the baseband unit and the remote radio head function.

However, such tight integration would not be possible without modification to the hardware and functionality of current baseband units. In order to solve this problem, Patent Document 2 discloses a method of estimating the communication demand and / or the user density distribution in the remote radio head without any help of the baseband unit. The technique is based on intercepting the radio interface bus and estimating the user density distribution from raw data flowing through the radio interface bus connecting the baseband unit and the remote radio head.

U.S. Pat. No. 9,485,770 U.S. Patent Application Publication No. 2016/0021650 European Patent Application Publication No. 2282574

Based on this background, as shown in Patent Document 2, a method of adaptively adjusting the coverage in the azimuth direction and / or the elevation angle direction without the assistance of the baseband unit or an external device is a method of adjusting the coverage of the baseband unit and the remote. It is necessary to intercept the bus of the wireless interface connected to the wireless head. Such a method is considered to be mechanically inefficient because it requires duplicating the bus decoding function of the wireless interface. Moreover, accurate timing and frame synchronization is required to estimate traffic demand and / or user density distribution by intercepting raw data passing through the bus of the radio interface between the remote radio head and the baseband unit. However, it is extremely important.

CPRI (Common Public Radio Interface) is an example of a bidirectional radio interface bus that connects such a remote radio head and a baseband unit. CPRI requires strict synchronization at an accurate timing of about 8.138 nanoseconds in order to accurately scramble and decode data with a remote radio head.

One object of the present disclosure is to provide a remote radio head that contributes to adaptively adjusting coverage to meet traffic demands in an architecturally efficient manner.

From the first viewpoint, it is a remote radio head including a plurality of antennas that generate a plurality of analog beams in a radio communication system that provides a service to at least one user terminal, and each RF chain (Radio Frequency Chain). Based on a metric calculator configured to calculate at least one metric that indicates traffic demand as a spatial function by using the signal of, and the at least one calculated metric. A remote radio head is provided, including a beam former, which is configured to generate an analog beam in the spatial direction of high traffic demand.

A second perspective is a beamforming method performed by a remote radio head equipped with a plurality of antennas that generate a plurality of analog beams in a radio communication system that provides services to at least one user terminal.
By using the signals of each RF chain (Radio Frequency Chain), at least one metric indicating traffic demand is calculated as a function in the spatial direction.
A beamforming method is provided that includes generating an analog beam in the spatial direction of high traffic demand based on at least one calculated metric.

A third perspective contains a program executed by a computer embedded in a remote radio head with multiple antennas that generate multiple analog beams in a radio communication system that services at least one user terminal. It ’s a storage medium,
By using the signals of each RF chain (Radio Frequency Chain), at least one metric indicating traffic demand is calculated as a function in the spatial direction.
A storage medium containing a program for causing the computer to generate an analog beam in the spatial direction of high traffic demand based on at least one calculated metric is provided. The program may be recorded on a storage medium that can be read by a computer. The storage medium may be a non-volatile storage medium such as a semiconductor storage device, a hard disk, a magnetic storage medium, or an optical storage medium. The present invention may be embodied as a computer program product.

According to the present disclosure, the remote radio head contributes to adaptively adjusting the coverage to meet the traffic demand in an architecturally efficient manner.

It is a figure which shows the outline of one Embodiment. It is a figure which shows an example of the mobile communication system including a plurality of user terminals and a base station. An example of a block diagram of a remote radio head in a base station is shown. An example of a block diagram of a remote radio head in a Time Division Duplex system is shown. An example of a block diagram of a remote radio head in a Frequency Division Duplex system is shown. An example of a block diagram of a remote radio head in a frequency division duplex system using antennas secured in an uplink and a downlink is shown. An example of a block diagram of a remote wireless head for receiving data via uplink is shown. An example of a block diagram of a remote wireless head for transmitting data via a downlink is shown. An example of a block diagram of an RF chain in a remote radio head is shown. An example of a block diagram of a remote radio head in a base station according to the first embodiment is shown. It is a flowchart for demonstrating the operation of the remote radio head in Embodiment 1. An example of a block diagram of a remote radio head for receiving data on the uplink in the first embodiment is shown. An example of a block diagram of a remote radio head for downlink data transmission in the first embodiment is shown. An example of the block diagram of the remote radio head in the base station according to the second embodiment is shown. It is a flowchart for demonstrating operation of the remote radio head in Embodiment 2. An example of a block diagram of a remote radio head for receiving data on the uplink in the second embodiment is shown. An example of a block diagram of a remote radio head for downlink data transmission in the second embodiment is shown. A block diagram for explaining the hardware configuration of the remote radio head is shown.

First, an outline of one embodiment is shown in FIG. For convenience, various components are indicated by reference characters in the following overview. That is, the following reference characters are used merely as an example to facilitate understanding of the present disclosure. Therefore, the present disclosure is not limited to the following summary description. Furthermore, the lines connecting the blocks in each drawing include both directions and one direction. The one-way arrow schematically shows the main signal (data) flow, but does not exclude interactivity. Further, in this document, "and / or" represents at least one of the former element and the latter element of this expression. For example, "item 1 and / or item 2" indicates "at least one of item 1 and item 2".

The remote radio head (RRH) 11 includes a plurality of antennas that generate a plurality of analog beams in a radio communication system that provides services to at least one user terminal. The remote radio head 11 includes a metric calculator 101 and a beam former 102 (beam former). The metric calculator 101 is configured to calculate at least one metric indicating traffic demand as a function in the spatial direction by using the signals of the respective RF chains. The beam shaper 102 is configured to generate a spatially oriented analog beam of high traffic demand based on the at least one calculated metric. The RF chain is a circuit module in which circuits for modulation or demodulation of analog and digital signals are cascaded.

The remote radio head 11 in a mobile communication system includes a metric calculator 101 configured to calculate at least one metric using signals associated with a radio frequency chain. For example, using one of the signals input to each radio frequency chain, the signal output from each radio frequency chain, and the signal in each radio frequency chain. , Calculate the metric. In addition, the signal for calculating the metric can be obtained in the analog or digital domain. The remote radio head 11 optimizes coverage by aligning analog beamforming towards areas of higher traffic demand (high user density distribution) in both the azimuth and elevation directions. Includes the configured beam former 102. Therefore, coverage is optimized for areas of higher traffic demand by analog beamforming to maximize user quality of service (QoS) and system throughput.

As a result, the remote radio head 11 eliminates the need for duplication of the decoder function of the radio interface and more precise synchronization with the encoder of the BBH (baseband unit). This is because the traffic demand is estimated from the signals of each RF circuit (RF chain). Moreover, the additional components needed to estimate traffic demand from the analog signals of each RF circuit are easily integrated into a single chip with a phased array antenna and are therefore relatively extremely compact. It becomes an architecture. That is, the remote radio head 11 adaptively adjusts coverage to traffic demand in an architecturally efficient manner.

<Embodiment>
The following description of this disclosure and its advantages aids further understanding. Hereinafter, embodiments of the present disclosure will be shown with reference to the drawings. In order to explain the present disclosure, an embodiment is configured assuming application to a mobile communication system.

First, the mobile communication system and the user terminal commonly used in the present disclosure will be described in detail with reference to FIGS. 2 and 9.

FIG. 2 illustrates an example of a mobile communication system including a radio base station (BTS: Base Transceiver Station) 1 and user terminals (UTs: User Terminals) 2. The fact that a single antenna is attached to the user terminal 2 is for the sake of explanation only, and in the present disclosure, a system may be equipped with an arbitrary number of antennas by those skilled in the art. The user terminal 2 is located in the radio coverage area of the radio base station 1, and can communicate with the radio base station 1 in both the up direction and the down direction.

The radio base station 1 includes a remote radio head 11 and a base band unit 13. The remote radio head 11 and the baseband unit 13 may be arranged at the same location or may be arranged at different locations, and both are connected to each other by a bidirectional wireless interface bus 12.

FIG. 3 is a diagram illustrating an example of the remote wireless head 11. Referring to FIG. 3, the remote radio head 11 includes an antenna (RRH antenna) 111, an RF front end 113, an RF chain 114, and a digital interface 115. The remote radio head 11 includes an L RF chain 114 and an L RF front end 113 (where L is the number of RF chains and RF front ends present within the remote radio head 11). The antenna 111 includes a plurality of sub-arrays 111a and a plurality of phase shifters (analog phase shifters) 112. Each subarray 111a including the plurality of antenna elements 11b is connected to the RF front end 113. The antenna 111 is used to receive an upward signal from the user terminal 2 and to send a downward signal to the user terminal 2. The reception of the uplink signal and the transmission of the downlink signal can be time or frequency-multiplexed under the control of the RF front end 113.

4 and 5 show an example of a Time Division Duplex (TDD) system and a Frequency Division Duplex (FDD) system, respectively, in a block diagram. For example, as shown in FIG. 4, in the case of the TDD system, since reception and transmission are controlled by the transmission / reception switch 1131, the same antenna 111 is used for both uplink signal reception and downlink signal transmission. be able to.

In the case of the FDD system, all the antennas 111 can be used for transmitting the downlink signal to the user terminal 2 and receiving the uplink signal from the user terminal 2. FIG. 5 illustrates an example of the remote radio head 11 of the FDD system. Since the duplexer 1135 separates the reception frequency component and the transmission frequency component, the downlink signal transmission and the uplink signal reception are performed simultaneously at different frequencies.

In addition to this, in the FDD system, as shown in FIG. 6, some of the antennas 111 can also be used exclusively for uplink reception and other antennas 111 are reserved for downlink signal transmission. Will be done.

Here, an example of the block diagram shown in FIG. 7 illustrates a remote radio head 11 for uplink reception only. In the case of only uplink reception, the signals received by each antenna element 111b in the phased array 111a are combined and integrated with all the antennas 111 by the combiner 1132.

As shown in FIG. 8, in the downlink transmission as well, the signal from each RF chain 114 is split by the splitter 1133.

Detailed block diagrams and operations of the RF front end 113 in both the TDD system and the FDD system are familiar to those skilled in the art, and therefore detailed description of the RF front end 113 will be omitted.

The total number of antennas 111 (N) is much larger than the number of RF chains 114 (L) (that is, N >> L). The connection between the antenna 111 and the RF chain 114 can be realized in various ways. One possible form is when all antennas 111 are connected to their respective RF chains, and the transmitted and / or received signals pass through all RF circuits. Such an architecture is referred to in the radio and mobile literature as a full-array architecture.

Another possible form is to divide the entire antenna 111 into subarrays of equal or different size, each subarray connecting to a separate RF chain 114. Such an architecture is known as a subarray architecture in the radio and mobile communications literature.

There may be several other approaches for connecting the antenna 111 to the RF chain 114, but those skilled in the art will readily appreciate this disclosure regardless of the approach or method of connecting the antenna 111 to the RF chain 114. Applicable.

Each antenna element 111b in the sub-array 111a is connected to the phase shifter 112. Although considered here for the sake of a linear array, the present disclosure is also valid for other array configurations such as rectangles, squares and / or circles. The signals received (transmitted) from the individual antenna elements 111b are phase-shifted and combined (split) to provide the output of the subarray 111a. This is called analog beamforming.

The remote radio head 11 applies one or more broader and / or multiple beamforming weights, including both phase shift and amplitude, to the antenna elements 111b in each subarray 111a. , A narrower beam can be generated, and the beam can be steered in any spatial direction. Here, the use of this phase shifter 112 is for explanatory purposes only, and the present disclosure is based on a system or other system using a butler matrix used by one of ordinary skill in the art to generate analog beamforming. You should know that it can be applied to similar networks in.

Here, it should be noted that the maximum number of simultaneous analog beams by the remote radio head 11 is always limited to the number of RF chains 114. In other words, at most L different spatial directions can be selected at the same time. However, L is the total number of RF chains 114.

Moreover, in the case of TDD systems, all analog beams are used for both uplink and downlink in different time slots. There, it is possible to adaptively determine and adjust where in one frame the uplink and downlink time slots are based on the requirements of the system. For this reason, more time slots are devoted to receiving the uplink to maximize uplink performance in the TDD system, and vice versa, less time slots are spent transmitting downlink data. Similarly for FDD systems, the width of the uplink and downlink frequency bands can be adaptively determined and adjusted based on the system requirements.

FIG. 9 is a block diagram of an example of an RF chain contained within the remote radio head 11. Referring to FIG. 9, the RF chain 114 includes a band pass filter 1141, a power amplifier 1142a, a low noise amplifier 1142b, an IF + RF up / down converter 1143, a low pass filter 1144, and an analog-to-digital converter. (ADC: Analog-to-Digital converter) and / or digital-to-analog converter (DAC: Digital-to-Analog converter) 1145 and. When data is transmitted to the user terminal 2, the RF chain 114 modulates the baseband signal into a radio frequency band. When receiving data from the user terminal 2, the RF chain 114 demodulates a signal in the radio frequency band to obtain a baseband signal.

According to FIG. 3 and the like, the digital interface 115 exchanges data with the baseband unit 13 via the bidirectional wireless interface bus 12.

The remote radio head 11 controls analog beamforming, along with uplinks and downlinks, in the direction of high traffic demand and / or the distribution of user density. Further details of this process can be obtained as described in the particular embodiments herein.

It is noted here that the present disclosure provides a technique for a remote radio head 11 that also communicates with any common baseband unit 13 and user terminal 2. More detailed block diagrams and operations of the baseband unit 13 and the user terminal 2 are well known to those skilled in the art and will be omitted in this document.

Each exemplary embodiment of the present disclosure will be described in corresponding order based on the description of the common systems and devices described above.

<Embodiment 1>
The details of the first embodiment will be described below with reference to the drawings.

In summary, in Embodiment 1, the remote radio head 11 monitors the signal flowing from the digital interface 115 to each RF chain 114 in the downlink and the signal flowing from each RF chain 114 to the digital interface 115 in the uplink. Providing technology. The remote radio head 11 then estimates at least one metric that represents the distribution of user density and / or traffic demand as a spatial function of analog beamforming. For example, the remote radio head 11 is powered from an in-phase component and a quadrature component of digital data flowing between the RF chain 114 and the digital interface 115 for the current spatial direction of analog beamforming. ) Calculate the level. The remote radio head 11 then compares the calculated metric (current estimate) with the previous history of previously calculated metric (stored estimate) across all other spatial directions. To do. Finally, the remote radio head redefines the preferred spatial orientation of the uplink and downlink to meet the user density distribution and / or traffic demand.

Hereinafter, the details of the first embodiment will be described with reference to FIGS. 10 to 13.

FIG. 10 shows an example of a block diagram of the remote wireless head 11 according to the first embodiment. Referring to FIG. 10, the remote radio head 11 further includes an integrated monitor / estimator 15, a storage unit 16, an analog beam selector 17, and a phase controller 18. The integrated monitor / estimator 15 is connected to the metric calculator 101 described above. The analog beam selector 17 and the phase controller 18 are connected to the beam shaper 102 described above.

<System operation>
FIG. 11 shows the operation of the entire system including the user terminal 2 and the remote wireless head 11. First, the remote radio head 11 selects a subset of analog beams from a plurality of analog beams defined by the designer and / or held by the remote radio head 11. The remote radio head 11 is capable of producing one or more analog beams with the same or different beam widths in both the azimuth and elevation planes when one or more beams can be aligned in a particular direction. Is. Here, it is assumed that some candidate analog beams have already been selected based on past knowledge of traffic demand and / or user density distribution. Therefore, in the first step S111, the remote radio head 11 uses appropriate analog beamforming to direct to a specific spatial direction and communicate with the candidate user terminal 2 on both the uplink and the downlink. Shown.

The integrated monitor / estimator 15 monitors the data flowing between each RF chain 114 and the digital interface 115 continuously or at predetermined intervals. The integrated monitor / estimator 15 calculates at least one metric that indicates the user density distribution and / or traffic demand as a spatial function of analog beamforming (operation S112). For example, such a metric is obtained by estimating the power level from the digital signal of each RF chain 114. More specifically, the calculation of one or more metrics is calculated by estimating the power level of digital data flowing from the digital interface 115 to each RF chain 114 in the case of downlinks and in the case of uplinks. On the contrary, it is calculated by estimating the power level of digital data flowing from each RF chain 114 to the digital interface 115.

The integrated monitor / estimator 15 updates the storage unit 16 after calculating the metric. The storage unit 16 that stores and tracks the calculated metrics in each spatial direction in both the uplink and the downlink is updated.

After calculating at least one metric, the integrated monitor / estimator 15 performs a comparison of the current spatially calculated metric of analog beam forming with the other previously calculated spatially calculated metric. The integrated monitor / estimator 15 subsequently categorizes their spatial orientations on both the uplink and the downlink, respectively, based on the comparison of the metrics on the uplink and the downlink (operation S113). More specifically, the integrated monitor / estimator 15 has a spatial direction higher than the current spatial direction metric for all section directions except the current spatial direction, and the current spatial direction. It is classified as having a metric lower than the metric of. The integrated monitor / estimator 15 then determines the spatial direction with the highest metric for each of the uplink and downlink as the preferred spatial direction. Here, if there is no direction with a higher metric, the current spatial direction is determined as the preferred spatial direction. In this way, the integrated monitor / estimator 15 determines the preferred spatial orientation in the uplink and downlink by comparing the currently estimated metric with the history of the metric.

The analog beam selector 17 selects, from among the determined (predetermined), a subset of the potential spatial direction with a relatively high calculated metric (operation S114). The analog beam selector 17 thus selects a subset of analog beamforming that achieves the determined preferred spatial orientation.

Finally, the phase controller 18 performs analog beamforming in the specified direction. The phase controller 18 steers an analog beam in a specific spatial direction by assigning appropriate beamforming weights to the phase shift and amplitude for each antenna element 111b (operation S115).

By repeatedly monitoring the data, determining the preferred spatial orientation, and changing the spatial orientation of the current analog beam, the current spatial orientation will eventually converge in the direction of the highest traffic demand. ..

Based on the description of the first embodiment, it is possible to adaptively adjust analog beamforming in elevation and azimuth planes without duplicating the coding / decoding functions of the digital interface. In addition, the user density distribution and / or the estimation of traffic demand does not require precise synchronization with the coded data of the baseband unit. This is because the digital signal flowing between the digital interface 115 and the RF chain 114 is used to calculate the metric.

Two examples are provided to better understand the operation of Embodiment 1.

<Example 1: Uplink reception only>
For simplicity, it is assumed that all subarrays 111a are used only for receiving uplink signals from user terminal (UT) 2. A block diagram which is an example of the remote radio head 11 according to the first embodiment is shown in FIG. This is generally applicable to both TDD and FDD systems.

According to the operation of Embodiment 1, the remote radio head 11 provides at least one metric indicating the user density distribution and / or traffic demand from the signal received on the uplink as a spatial function of analog beamforming. presume. Such a metric is obtained by calculating the power level of the uplink received signal flowing from each RF chain 114 to the digital interface 115. Using the mathematical representation of the related technology of the mobile communication system, the metric calculated from the digital signal of the RF chain # l (1st RF chain 114) in the remote radio head 11 is expressed by the following formula. ..

対応する最適化関数は以下で表される。

The corresponding optimization function is represented below.

はｌ番目のサブアレイ１１１ａの空間方向

のアナログビームフォーミングによる受信信号から推定された電力レベルのメトリックを表している。ここに、

と、

は、それぞれｂ番目のビームの方向の方位角と仰角である。
ｂ_{ｍａｘ，ｌ}は、ｌ番目のサブアレイ１１１ａのアナログビームフォーミングのビーム方向の候補のインデックスを示している。
Ｉ_ｌ（ｎ）とＱ_ｌ（ｎ）は、時刻ｎにおけるＲＦチェーン＃ｌのデジタル信号の同位相と直交位相との成分である。なお、メトリックを計算するために電力レベルを使用しているのは、単に説明を簡単とするためである。リモート無線ヘッド１１における動作Ｓ１１３からＳ１１５は、前述しているため、詳細な説明は、簡潔さのためにここでは省略する。

Is the spatial direction of the l-th subarray 111a

It represents a metric of power level estimated from the received signal by analog beamforming of. here,

When,

Are the azimuth and elevation angles in the direction of the b-th beam, respectively.
b _{max and l} indicate indexes of beam direction candidates for analog beamforming of the l-th subarray 111a.
_Il (n) and Q _l (n) are components of the in-phase and quadrature phases of the digital signal of the RF chain # _{l at} time n. It should be noted that the power level is used to calculate the metric simply for the sake of simplicity. Since the operations S113 to S115 in the remote radio head 11 are described above, detailed description thereof will be omitted here for the sake of brevity.

<Example 2: Downlink transmission only>
For simplification of the second embodiment, it is assumed that all subarrays 111a are used only for transmitting downlink signals towards the user terminal 2. FIG. 13 shows a block diagram which is an example of the remote radio head 11 in the second embodiment under this assumption. These are usually applicable to both TDD and FDD systems.

According to the processing of the first embodiment, the remote radio head 11 first estimates from the transmitted downlink signal as a spatial function of analog beamforming, at least one metric representing user density distribution and / or traffic demand. When the Maximum Ratio Transmission (MRT) method is adopted for downlink data transmission of baseband unit 13, such a metric estimates the power level of each data in the RF chain 114. It is calculated based on. More precisely, if the transmitter is a transmitter with more than one transmitting antennas and / or subarrays that transmit the same data in parallel, the respective antennas and / or / Or the subarray is weighted by a scale factor proportional to the complex channel coefficient between the transmitting and receiving antennas. By using the mathematical notation in the related technology of mobile communication systems, the scale factor of subarray # l is expressed by the following equation.

送信された信号

はベースバンドユニット１３から送信される信号ベクトルであり、次式で表される。

Transmitted signal

Is a signal vector transmitted from the baseband unit 13, and is expressed by the following equation.

ここで、ｈ_ｌはユーザ端末（ＵＴ）２とサブアレイ＃ｌとの間の複素チャンネル係数を示している。

はｈ_ｌの複素共役（complex conjugate）を示す。数式４のＨはエルミート転置を示す。

はダウンリンクにおいて送信するためのデータシンボルであり、

はベースバンドユニット１３から送信される信号ベクトル

を生成するために適用される重みベクトルである。実施例１と同様に、送信する信号ベクトルである

の要素から電力を計算することにより、ユーザ密度分布、及び／又は、トラフィック需要を推定することが可能である。
Ｓ_ｌをＲＦチェーン＃１の送信信号とすると、ＲＦチェーン＃１の計算されたメトリックは、次式で表される。

Here, h _l indicates the complex channel coefficient between the user terminal (UT) 2 and the subarray # _l .

Denotes the complex conjugate (complex conjugate) of _{h l.} H in Equation 4 indicates Hermitian transpose.

Is a data symbol for transmission on the downlink,

Is the signal vector transmitted from the baseband unit 13.

Is a weight vector applied to generate. Similar to the first embodiment, it is a signal vector to be transmitted.

By calculating the power from the elements of, it is possible to estimate the user density distribution and / or the traffic demand.
_Assuming that S _l is the transmission signal of RF chain # 1, the calculated metric of RF chain # 1 is expressed by the following equation.

対応する最適化関数は次式で表される。

The corresponding optimization function is expressed by the following equation.

はｌ番目のサブアレイ１１１ａの空間方向

のアナログビームフォーミングによる送信信号から推定された電力レベルのメトリックを表しており、ここに、

と

とは、それぞれｂ番目のビームの方向の方位角と仰角である。ｂ_{ｍａｘ，ｌ}はｌ番目のサブアレイ１１１ａのアナログビームフォーミングのビーム方向の候補のインデックスを示している。実施形態１におけるリモート無線ヘッド１１の動作Ｓ１１３からＳ１１５は、前述しているため、詳細な説明は、簡潔さのためにここでは説明を省略する。

Is the spatial direction of the l-th subarray 111a

Represents a metric of power level estimated from the transmitted signal by analog beamforming in.

When

Is the azimuth and elevation in the direction of the b-th beam, respectively. b _{max and l} indicate indexes of beam direction candidates for analog beamforming of the l-th subarray 111a. Since the operations S113 to S115 of the remote radio head 11 in the first embodiment are described above, detailed description thereof will be omitted here for the sake of brevity.

<Embodiment 2>
In summary, the second embodiment makes one modification to the first embodiment. In the second embodiment, it is introduced to calculate at least one metric indicating the user density distribution and / or the traffic demand from the analog signal of each RF chain 114. For example, the remote radio head 11 calculates the power level from the analog signals in each RF chain 114 and / or the analog signals between the RF front end 113 and the RF chain 114, respectively.

After comparing the power estimated from the current analog signal with the history, the remote radio head 11 redefines a more preferred spatial direction for data reception on the uplink and data transmission on the downlink.

Based on these additions, Embodiment 2 modifies the functionality of the hardware element used to calculate the traffic demand and / or the metric representing the user density distribution as a function in the spatial direction. ing.

Hereinafter, the details of the second embodiment will be described with reference to FIGS. 14 to 17.

FIG. 14 shows a block diagram forming an example of the remote radio head 11 according to the second embodiment. Referring to FIG. 14, the remote radio head 11 includes an integrated monitor / estimator 19 instead of the integrated monitor / estimator 15. The integrated monitor / estimator 19 is different from the integrated monitor / estimator 15 in that it monitors an analog signal.

FIG. 15 shows the processing of the entire system including both the remote wireless head 11 and the user terminal 2. In the first operation S111, a subset of spatially oriented candidates for analog beamforming is selected and communicated with the user terminal 2 on both the uplink and downlink. Since this process is described in the first embodiment, detailed description thereof will be omitted for the sake of brevity.

The integrated monitor / estimator 19 displays data flowing through each of the RF chains 114 and / or data flowing between the RF chain 114 and the RF front end 113 continuously or at pre-defined intervals. Monitor. The integrated monitor / estimator 19 calculates at least one metric indicating traffic demand and / or user density distribution as a function of the current spatial direction of analog beamforming (operation S112a).

For example, such a metric can be obtained by calculating the power level of the analog signal at the output of the DAC or the input of the ADC contained in the ADC / DAC1145, respectively, on the downlink and uplink. In addition, such metrics are between the ADC / DAC 1145 and the low pass filter 1144, or between the low pass filter 1144 and the IF + RF Up / Down converter 1143, and / or the block of RF chain 114, also shown in FIG. It can also be calculated from analog data flowing between any two components of the RF chain 114 mentioned or not mentioned in the example of the figure.

Similarly, in downlinks and uplinks, power can be calculated from analog signals at the outputs and inputs of each RF chain 114. In other words, in the downlink, the power is estimated from the signal flowing out from each RF chain 114 to each RF front end 113, and in the uplink, the power is estimated from the signal flowing out from each RF front end 113 to each RF chain 114. Can be done.

The last three processes, the process of determining the spatial direction of the uplink and downlink based on the comparison of power (operation S113), and
Processing to select the spatial direction of analog beamforming from a set of candidates (operation S114),
The process (operation S115) of appropriately applying the weighting of beamforming for both the phase shift and the amplitude to each phase shifter in order to direct the beam in a specific direction is the same as that of the first embodiment. For this reason, detailed description of these processes will be omitted for brevity.

In addition, as in the first embodiment, in the second embodiment, all the sub-arrays 111a can be used exclusively for receiving the uplink signal from the user terminal 2 (FIG. 16). Further, as in the first embodiment, in the second embodiment, all the sub-arrays 111a can be used exclusively for transmitting the downlink signal to the user terminal 2 (FIG. 17).

Based on the description of the second embodiment, it is possible to conclude that the second embodiment is a further improvement of the first embodiment. In particular, using an analog signal to calculate the metric makes the configuration (architecture) of the remote radio head 11 compact. It easily integrates the external components used to estimate traffic demand and / or user density distribution into the phaser network in a single chip configuration ( This is because it can be integrated).

The application of the first embodiment and the second embodiment is not limited to the cases used in the above description. On the contrary, the essences of Embodiment 1 and Embodiment 2 can be applied to various situations by those skilled in the art.

The function of the remote radio head 11 (eg, the integrated monitor / estimator 15) may be realized by a processor incorporated in the remote radio head 11 (see FIG. 18). For example, the remote wireless head 11 includes a CPU (Central Processing Unit) 51 and a memory 52. For example, a processing module such as the integrated monitor / estimator 15 can be realized by the CPU 51 executing a program stored in the memory 52. In addition, the program may be updated via a network or storage medium containing the program.

As mentioned above, the present disclosure applies to analog-digital hybrid beamforming configurations in which a subset of antennas share a single, common RF chain. Also, the present disclosure is not limited to the received uplink signal. It can also be easily applied to downlink signals to estimate downlink traffic in a network (eg, Example 2: downlink transmission only). In addition, the disclosure proposes stand-alone processing of radio units with no communication or interaction between radio units and baseband units to estimate traffic demand.

In addition, the disclosure directs the analog beam to areas of higher traffic demand, taking into account both uplink and downlink. More precisely, more analog beams are directed to areas of higher uplink traffic in order to maximize uplink performance. Similarly, place more analog beams in areas of higher downlink traffic demand to minimize downlink performance.

The preferred embodiment will be described below.

(Form 1)
The first aspect is the same as the remote radio head which is based on the first viewpoint.
(Form 2)
The metric calculator is a remote of Form 1 configured to calculate the metric using a downward digital signal input to each RF chain or an upward analog signal input to each of the RF chains. Wireless head.
(Form 3)
The metric calculator according to the first embodiment is configured to calculate the metric using an upward digital signal output from each of the RF chains or a downward analog signal output from each of the RF chains. Remote wireless head.
(Form 4)
The metric calculator is a remote radio head of the first embodiment configured to calculate the metric using signals flowing inside each of the RF chains.
(Form 5)
The metric calculator is a remote radio head of any one of Form 1 to Form 4 configured to calculate the metric using the power level of the signal from each of the RF chains.
(Form 6)
The metric calculator is a remote radio head of embodiment 5 configured to calculate the metric using the power level of the signal from the RF chain of each of the digital regions.
(Form 7)
The metric calculator is a remote radio head of embodiment 5 configured to calculate the metric using the power level of the signal from the RF chain in each of the analog regions.
(Form 8)
The beam shaper is a remote radio head of any one of Form 1 to Form 7 configured to select a subset of candidate beams that match the traffic demand from a predetermined candidate beam set.
(Form 9)
The beam shaper is a remote radio head of embodiment 8 configured to select a subset of candidate beams that match the traffic demand from multiple candidate beams and the user density distribution in both the azimuth and elevation directions. ..
(Form 10)
The metric calculator is any one of Form 1 to Form 9 configured to compare the calculated current spatial metric with the previously calculated spatial metric excluding its current spatial direction. Remote wireless head.
(Form 11)
The metric calculator is a remote radio head of embodiment 10 configured to determine a suitable spatial direction for uplink and downlink communications based on the results of the comparison.
(Form 12)
The remote radio head according to any one of Form 1 to Form 11, further comprising a storage unit for storing the calculated metric in each of the spatial directions.
(Form 13)
Form 13 is the same as the beamforming method from the second viewpoint.
(Form 14)
Form 14 is the same as the program from the third viewpoint.

The disclosures of the patent documents presented above are incorporated herein by reference to this description. Embodiments may be modified and adjusted within the scope disclosed (including claims) throughout the invention, based on basic technical concepts. Within the scope of the claims of the present invention, various disclosed elements may be selected and combined in various ways. That is, it should be understood that those skilled in the art are required to include modifications, selections and combinations of elements made within the scope of the entire disclosure of the present invention.

1 Wireless base station 2 User terminal 11 Remote wireless head 12 Bidirectional wireless interface bus 13 Baseband unit 15, 19 Integrated monitor / estimator 16 Storage unit 17 Analog beam selector 18 Phase controller 51 CPU
52 Memory 101 Metric Calculator 102 Beam Shaper 111 Radio Base Station Antenna 111a Sub Array 111b Antenna Element 112 Phase Shifter (Phase Shifter)
113 RF Front End 114 RF Chain 115 Digital Interface 1131 Transmit / Receive Switch 1132 Combiner 1133 Splitter 1135 Duplexer 1141 Band Passband Filter 1142a Power Amplifier 1142b Low Noise Amplifier 1143 IF + RF Up / Down Converter 1144 Low Pass Filter 1145 Analog-Digital Converter / Digital-Analog Conversion vessel

The present invention relates to a remote radio head (RRH: Remote Radio Head), a beamforming method, and a program thereof. In particular, it relates to remote radio heads, beamforming methods and programs for estimating traffic demand.

A third perspective contains a program executed by a computer embedded in a remote radio head with multiple antennas that generate multiple analog beams in a radio communication system that services at least one user terminal. It ’s a storage medium,
By using the signals of each RF chain (Radio Frequency Chain), at least one metric indicating traffic demand is calculated as a function in the spatial direction.
A program is provided to cause the computer to generate an analog beam in the spatial direction of high traffic demand based on at least one calculated metric. The program may be recorded on a storage medium that can be read by a computer. The storage medium may be a non-volatile storage medium such as a semiconductor storage device, a hard disk, a magnetic storage medium, or an optical storage medium. The present invention may be embodied as a computer program product.

はｌ番目のサブアレイ１１１ａの空間方向

のアナログビームフォーミングによる受信信号から推定された電力レベルのメトリックを表している。ここに、

と、

は、それぞれｂ番目のビームの方向の方位角と仰角である。
ｂ_{ｍａｘ，ｌ}は、ｌ番目のサブアレイ１１１ａのアナログビームフォーミングのビーム方向の候補のインデックス（γ _ｌ （φ _ｂ , θ _b ）の最大値を与える引数ｂ）を示している。
Ｉ_ｌ（ｎ）とＱ_ｌ（ｎ）は、時刻ｎにおけるＲＦチェーン＃ｌのデジタル信号の同位相と直交位相との成分である。なお、メトリックを計算するために電力レベルを使用しているのは、単に説明を簡単とするためである。リモート無線ヘッド１１における動作Ｓ１１３からＳ１１５は、前述しているため、詳細な説明は、簡潔さのためにここでは省略する。

Is the spatial direction of the l-th subarray 111a

It represents a metric of power level estimated from the received signal by analog beamforming of. here,

When,

Are the azimuth and elevation angles in the direction of the b-th beam, respectively.
b _{max and l} indicate the index of the candidate in the beam direction of the analog beamforming of the l-th subarray 111a ( argument b that gives the maximum value of γ _l (φ _b , θ _b )) .
_Il (n) and Q _l (n) are components of the in-phase and quadrature phases of the digital signal of the RF chain # _{l at} time n. It should be noted that the power level is used to calculate the metric simply for the sake of simplicity. Since the operations S113 to S115 in the remote radio head 11 are described above, detailed description thereof will be omitted here for the sake of brevity.

Claims (14)

A remote wireless head comprising a plurality of antennas that generate a plurality of analog beams in a wireless communication system that provides services to at least one user terminal.
A metric calculator configured to use the signals of each RF chain (Radio Frequency Chain) to calculate at least one metric that indicates traffic demand as a function in the spatial direction. When,
A beam former configured to generate an analog beam in the spatial direction of high traffic demand based on at least one calculated metric.
Remote wireless head including. The metric calculator is configured to calculate the metric using a downward digital signal input to each of the RF chains or an upward analog signal input to each of the RF chains. The remote wireless head according to 1. The metric calculator is configured to calculate the metric using an ascending digital signal output from each of the RF chains or a descending analog signal output from each of the RF chains. The remote wireless head according to 1. The remote radio head according to claim 1, wherein the metric calculator is configured to calculate the metric using signals flowing inside each of the RF chains. The remote radio head according to any one of claims 1 to 4, wherein the metric calculator is configured to calculate the metric using the power level measured from the signal of each of the RF chains. The remote radio head of claim 5, wherein the metric calculator is configured to calculate the metric using the power level measured from the signal of each of the RF chains in the digital domain. The remote radio head of claim 5, wherein the metric calculator is configured to calculate the metric using the power level measured from the signal of each of the RF chains in the analog domain. The remote radio head according to any one of claims 1 to 7, wherein the beam shaper is configured to select a subset of candidate beams that meet the traffic demand from a determined set. 8. The remote radio head of claim 8, wherein the beam shaper is configured to select the subset of candidate beams that match the traffic demand and the distribution of users in both the azimuth and elevation directions. .. The metric calculator is any of claims 1-9 configured to compare the calculated current spatial metric with a previously calculated spatial metric excluding the current spatial metric. The remote wireless head described in Kaichi. The remote radio head of claim 10, wherein the metric calculator is configured to determine preferred spatial orientations in the uplink and downlink based on the results of the comparison. The remote radio head according to any one of claims 1 to 11, further comprising storage for storing the calculated metrics for each spatial direction. A beamforming method performed by a remote radio head equipped with a plurality of antennas that generate a plurality of analog beams in a radio communication system that provides services to at least one user terminal.
By using the signals of each RF chain (Radio Frequency Chain), at least one metric indicating traffic demand is calculated as a function in the spatial direction.
A beamforming method comprising generating an analog beam in the spatial direction of high traffic demand based on at least one calculated metric. A storage medium that stores a program executed by a computer embedded in a remote wireless head having a plurality of antennas that generate a plurality of analog beams in a wireless communication system that provides a service to at least one user terminal.
By using the signals of each RF chain (Radio Frequency Chain), at least one metric indicating traffic demand is calculated as a function in the spatial direction.
Generates an analog beam in the spatial direction of high traffic demand, based on at least one calculated metric.
A storage medium containing a program for causing the computer to execute such a thing.

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